“Let all bitterness, and wrath, and anger, and clamour, and evil speaking, be put away from you, with all malice: And be ye kind one to another, tenderhearted, forgiving one another, even as God for Christ's sake hath forgiven you.” - Ephesians 4:31, 32.
People speak evil of others because of anger. The anger may be spontaneous or may have been stored in the mind which leads to bitterness, hatred, resentment, jealousy, lie-telling among other vices. “Let no corrupt communication proceed out of your mouth,” said St. Paul, “but that which is good to the use of edifying, that it may minister grace unto the hearers.” - Ephesians 4:29
Instead of reading minds, making rash judgments, harbouring grudges or vexation against our neighbours who may even be innocent, our Lord Jesus Christ enjoined his disciples to call the attention of the person who had wronged them to the error or fault. Furthermore, he said we could go further by inviting two or three people and thereafter the elders of the Church. (Matthew 18:15-17) These steps are to ensure that we settle issues we have with one another and work together with one mind. St. Paul declared, “Wherefore putting away lying, speak every man truth with his neighbour: for we are members one of another. Be ye angry, and sin not: let not the sun go down upon your wrath: Wherefore putting away lying, speak every man truth with his neighbour: for we are members one of another. Be ye angry, and sin not: let not the sun go down upon your wrath: Neither give place to the devil.” - Ephesians 4:25-27.